In the nacelle of a wind turbine, several heavy wind turbine components, such as gears, shafts, generators, etc., are arranged. From time to time, these components need maintenance, repair, or even replacement, and it is therefore often necessary to lower the components down from the nacelle and subsequently hoist them up again for installation in the nacelle.
In the prior art, several solutions are known for lowering wind turbine components down from the nacelle and hoisting them up. In one prior art solution, a typical crane at ground level is being used. However, since wind turbines are continually increasing in size, the components of the individual wind turbine are also increasing in sizes. Accordingly, typical cranes at ground level also need to be of a size where it is possible to handle the heavy components of the wind turbine. Thus, the costs for lowering and hoisting the components of the wind turbine by using ordinary ground-based cranes increase with the size of the wind turbine and the weight of the components which need to be handled. There is thus a need for a more cost-effective way of handling, i.e. lowering and hoisting, components from and to the nacelle.
In other solutions in the prior art, service cranes are permanently mounted either on the hub or the nacelle of the wind turbine. However, this increases the weight of the nacelle and thus the load on the tower of the wind turbine. In other solutions, the nacelle and the hub are arranged with crane foundations and attachment points, thus enabling service cranes to be lifted up and mounted on these foundations and attachment points when a service crane is necessary for the handling of the components from or to the nacelle. However, these foundations and attachments points must be provided with additional support and strengthening support so that the service crane may handle high loads, which also increase the weight of the nacelle and thereby the load placed on the tower of the wind turbine.